To clarify, there is a difference between a normal eSATAp/USB connection and a eSATA connection. The first provides power to the connected device, the second does not, but still requires to conform to a set of power specifics and laptops on the Mobo are not built the same way, same power, as the laptop Mobo, which is centered around conserving power usage.
http
/en.wikipedia.org/wiki/Serial_ATA - Scroll to half down the entire page.
The differences are:
Minimum transmit amplitude increased: Range is 500–600 mV instead of 400–600 mV.
Minimum receive amplitude decreased: Range is 240–600 mV instead of 325–600 mV.
Maximum cable length increased to 2 metres (6.6 ft) (USB and FireWire allow longer distances.)
The eSATA cable and connector is similar to the SATA 1.0a cable and connector except:
The eSATA connector is mechanically different to prevent unshielded internal cables from being used externally. The eSATA connector discards the "L"-shaped key and changes the position and size of the guides.
The eSATA insertion depth is deeper: 6.6 mm instead of 5 mm. The contact positions are also changed.
The eSATA cable has an extra shield to reduce EMI to FCC and CE requirements. Internal cables do not need the extra shield to satisfy EMI requirements because they are inside a shielded case.
The eSATA connector uses metal springs for shield contact and mechanical retention.
The eSATA connector has a design-life of 5,000 matings; the ordinary SATA connector is only specified for 50.
....
Desktop computers without a built-in eSATA interface can install an eSATA host bus adapter (HBA); if the motherboard supports SATA, an externally available eSATA connector can be added. Notebook computers can be upgraded with Cardbus[36] or ExpressCard[37] versions of an eSATA HBA. With passive adapters, the maximum cable length is reduced to 1 metre (3.3 ft) due to the absence of compliant eSATA signal-levels.
That second part is noted here:
http
/en.wikipedia.org/wiki/ESATAp
+12 V issue[edit]
There are only two versions of this port. Most laptop computers do not have +12V power available, and have an eSATAp port which provides only +5 V. Desktop computers, with +12V available, have a port with two additional pads, placed against the plug's "horns", which provide +12 V. Some manufacturers refer to these ports as eSATApd, where d stands for "dual voltage". Some devices, such as 2.5-inch drives, can operate off the +5V supplied by laptop eSATAp ports. Others, such as 3.5-inch drives, also require +12V; they can be powered from a desktop eSATAp port, but require an external +12V power supply if used with a laptop computer. This can lead to confusion if users are not aware of the distinction.
eSATAp PCI and PCI-e add-on cards are available for desktop computers. They usually provide two eSATAp ports, with port multiplier functionality, and hot-swap capability.
eSATAp cables are available with wide connectors to plug directly into the power and signal connectors of a bare drive, providing a +12V supply in the case of a desktop machine. A version of this wide connector is found inside every external sata hard drive enclosure; when the hard drive is slid inside, it mates with a connector that supplies it with both signal and power.
If the smaller side of this cable is plugged into a "powered" esata port, providing both 12 volts and 5 volts, then the wide end may be plugged into a 2.5" or 3.5" sata hard drive, supplying the bare drive with both signal and power. The small 2.5" drive will get signal and power at 5 volts, which is all that the smaller drive requires, and which the larger 3.5" drive requires only for its logic board. Additionally, the larger 3.5" drive will get the 12 volts it needs to power its disk spindle motor. Thus a bare hard drive may be conveniently placed directly on top of the computer, or on an adjacent table, and powered by the unique cable, it will run at full sata speeds, without the necessity of placing the hard drive into an external enclosure ((Aka external Power)).